In a large pot, add the peeled and cubed potatoes along with the finely diced celery. Fill the pot with enough salted water to cover the ingredients. Bring to a rolling boil and cook for 12-15 minutes, or until fork-tender.

Carefully drain the pot in a colander, allowing steam to escape. Return the potatoes and celery to the pot over low heat for about a minute to evaporate remaining water.

Off the heat, add the butter to the warm mixture, allowing it to melt. Mash the vegetables until smooth, gradually pouring in the milk until creamy.

Stir in salt, black pepper, and optional garlic. Taste and adjust seasoning as desired. Mix gently to combine.

Transfer to a serving bowl. Optionally top with a pat of butter or fresh herbs. Serve warm.